Aug 23, 2022

Benchmark Problems for Transcranial Ultrasound Simulation: Intercomparison of Compressional Wave Models

Jean-Francois Aubry, Oscar Bates, Christian Boehm, Kim Butts Pauly, Douglas Christensen, Carlos Cueto, Pierre Gelat, Lluis Guasch, Jiri Jaros, Yun Jing, Rebecca Jones, Ningrui Li, Patrick Marty, Hazael Montanaro, Esra Neufeld, Samuel Pichardo, Gianmarco Pinton, Aki Pulkkinen, Antonio Stanziola, Axel Thielscher, Bradley Treeby, and Elwin van 't Wout, Journal of the Acoustical Society of America 2022, Volume 152, Issue 2, Article No. 1003, online 16 August 2022; doi: 10.1121/10.0013426

Computational models of acoustic wave propagation are frequently used in transcranial ultrasound therapy, for example, to calculate the intracranial pressure field or to calculate phase delays to correct for skull distortions. To allow intercomparison between the different modeling tools and techniques used by the community, an international working group was convened to formulate a set of numerical benchmarks. In the published study, 9 different benchmarks of increasing geometric complexity are presented and defined, along with intercomparison results. The benchmarks include a single-layer planar bone immersed in water, a multi-layer bone, and a whole skull. Two transducer configurations — a focused bowl and a plane piston operating at 500 kHz — are considered, giving a total of 18 benchmark permutations. Eleven different modeling tools were used to compute the benchmark results. The models span a wide range of numerical techniques, including the finite-difference time-domain, angular spectrum, pseudospectral, boundary-element, and spectral-element methods. Good agreement is found between the models, particularly for the therapeutically relevant position, size, and magnitude of the acoustic focus within the skull. Cross-comparison of the results for each model with every other model indicates that the median values for each benchmark for the difference in focal pressure and position were found to be below 10% and 1 mm, respectively. The benchmark definitions, model results, and intercomparison codes are freely available to facilitate further comparisons and verification of 3rd-party modeling tools.

The scientific and technical impact of the study can be summarized as:

  • The IT’IS Foundation was involved in the study design and the definition of the benchmarks
  • A set of well-defined and reproducible numerical benchmarks relevant for the assessment of the simulation quality in transcranial ultrasound were developed that provide information about the numerical uncertainties associated with computational modeling, as well as for verification of acoustic simulation software
  • The intercomparison results show close agreement of the results from the modeling tools investigated, particularly regarding prediction of the acoustic focus position, size, and magnitude after propagation through and distortion by the skull, despite the wide variety of numerical techniques applied
  • The results build confidence in the ability of computational models to consistently predict exposure by transcranial focused ultrasound and demonstrate the reliability of the Sim4Life acoustic solver
  • The benchmark definitions and associated data files, simulation results, and codes to compute the intercomparison metrics are all freely available, allowing the results to be replicated, further analyses to be conducted, and verification of 3rd-party acoustic modeling tools
  • Continuation of this effort is ongoing, and benchmarks for elastic wave modeling and personalized modeling based on material parameters derived from patient computed tomography images will be addressed